Screening and Optimization of Indole-3-Acetic Acid Production and Phosphate Solubilization from Rhizobacteria Aimed at Improving Plant Growth

Abstract

A total of 216 bacterial strains were isolated from rice rhizospheric soils in Northern Thailand. The bacterial strains were initially tested for solubilization of inorganic phosphate, indole acetic acid (IAA) production, selected strains were then tested for optimized conditions for IAA production and whether these caused stimulatory effects on bean and maize seedling growth. It was found that all strains had solubilized inorganic phosphate (P), but only 18.05% produced IAA. The best IAA producer was identified by biochemical testing and 16S rDNA sequence analysis as Klebsiella SN 1.1. In addition to being the best IAA producer, this strain was a high P-solubilizer and produced the highest amount of IAA (291.97 ± 0.19 ppm) in culture media supplemented with L-tryptophan. The maximum production of IAA was achieved after 9 days of incubation. The culture requirements were optimized for maximum IAA production. The tested of IAA production by selected isolates was studied in a medium with 0, 0.1, 0.2, 0.5, 0.7, and 0.9% (v/v) L-tryptophan. Low levels (12.6 ppm) of IAA production was recorded without tryptophan addition. Production of IAA in Klebsiella SN 1.1 increased with an increase to 0.2% (v/v) tryptophan concentration. The production of IAA was further confirmed by extraction of crude IAA from this isolate and subsequent Thin Layer Chromatography (TLC) analysis. A specific spot from the extracted IAA production was found to correspond with a standard spot of IAA with the same R (f) value. The Klebsiella strain SN 1.1 also demonstrated stimulatory effects on bean seedlings in vivo.

A simple method for simultaneous RP-HPLC determination of indolic compounds related to bacterial biosynthesis of indole-3-acetic acid

“…The limits of detection for all studied analytes were below 0.015 μg mL −1 (Table 1). These results, together with the fact that the concentrations of indolic compounds accumulating in bacterial cultures typically reaches from a few to several dozens of μg mL −1 (Ahmad et al 2005; Khakipour et al 2008; Chaiharn and Lumyong 2011), indicate that no additional enrichment of the biological sample is required. Therefore, instead of time- and reagent-consuming organic solvent extraction, we utilized a single centrifugal filtration step for sample preparation.…”

Isolation and characterization of phosphate solubilizing bacteria (Klebsiella oxytoca) with enhanced tolerant to environmental stress

“…and Bacillus sp. However, Chaiharn and Lumyong (2011) reported extremely high IAA production (291.97 g/ml) and phosphate solubilization (334 g/ml) with strain Klebsiella SN 1.1 isolated from rice rhizospheric soils in Northern Thailand. It has been reported that microbial IAA promotes root growth either directly by stimulating plant cell elongation or cell division or indirectly by its influence on the ACC deaminase activity (Patten and Glick, 2002).…”

Mineral Phosphate Solubilization: Concepts and Prospects in Sustainable Agriculture

“…Besides, the production of chelating substances H 2 S, CO 2 , mineral acids, siderophores, biologically active substances like indole acetic acid [119], gibberellins and cytokinins Penicillium bilaii Citric and oxalic acid [105] Penicillium regulosum Citric and gluconic acid [106] Pseudomonas aeruginosa Gluconic [97] Pseudomonas putida Gluconic acid [107] Pseudomonas sp. Citric, gluconic [108] Pseudomonas sp.…”